Color-plus-clear coating systems involving the application of a colored or pigmented base coat to a substrate followed by the application of a transparent or clear topcoat to the base coat have become very popular as original finishes for automobiles. The color-plus-clear systems have outstanding gloss and distinctness of image. The clear coat is particularly important for these properties. However, such systems require the application of two coating layers and the use of two sets of application equipment.
Coating systems that employ hydroxy-aminoplast cure mechanisms are well known in the coating technology and provide many excellent coating properties. They are inexpensive and attractive, but it is widely recognized that such coatings have poor resistance to etching by acid. Acid etch resistance in coatings is becoming an increasingly desirable property, particularly for automotive coatings. Aminoplast cured coating systems of the prior art are not highly effective for providing protection against etching caused by acid rain. Moreover, when applied as a high gloss monocoat, such systems have been shown to fade, blush, crack, and/or lose gloss upon prolonged exposure to harsh ultraviolet (UV) light and humidity conditions.
Menovcik et al. in U.S. Pat. No. 5,475,064 discloses coating compositions containing aminoplasts and specific carbamate functional polyesters. These polyesters have pendant carbamate functionality and the reference does not disclose the use of the coatings for improved acid etch resistance or durability.
Culbertson et al. in U.S. Pat. No. 4,279,833 discloses specific carbamate functional acrylic monomers, polymers prepared therefrom, and coating compositions containing aminoplasts and these acrylic polymers. The reference does not disclose the use of such coating compositions as high gloss monocoats, nor does the reference recognize any advantage of carbamate functional polymers in coating compositions to improve acid etch resistance or durability.
Parekh in U.S. Pat. No. 4,543,276 discloses coating compositions containing urethane compounds and any of a number of polymers having any of various functional groups including carbamate. The reference does not disclose the use of such coating compositions as high gloss monocoats, nor does the reference recognize any advantage of carbamate functional polymers in coating compositions to improve acid etch resistance or durability.
It is desirable to provide a coating composition suitable for use as a high gloss monocoat that does not require application of a separate clear coat, utilizing inexpensive aminoplast curing agents yet having improved acid etch resistance properties and durability.